The present invention relates to safety mechanisms for blocking the travel of electrical air break switches, and in particular to mechanisms for blocking the travel of large, high-voltage electrical air break switches such as commonly found in electrical power substations.
A number of different mechanisms to prevent the opening or closing of electrical switches are known in the art. Such devices are primarily employed for the purpose of safety to personnel in the area of the switch, or in the area of the equipment that is powered by electricity fed through the switch. It is often the case that an electrical switch is located in a position remote from such equipment, and inadvertent operation of the switch may cause serious injury to persons attempting to repair the equipment that may become suddenly energized. Likewise, inadvertent application of power to equipment that has not been readied to receive current may cause significant damage to the equipment.
A number of safety mechanisms have been developed for standard knife switches, circuit breakers, and other types of switches commonly encountered. Such mechanisms are taught, for example, by U.S. Pat. No. 1,558,628 to Purcell; U.S. Pat. No. 1,281,127 to Blankenship; U.S. Pat. No. 1,298,745 to Lum; U.S. Pat. No. 1,092,259 to Ham; U.S. Pat. No. 1,774,540 to Alsaker et al.; and U.S. Pat. No. 4,882,456 to Hovanic et al. One significant disadvantage of each of these mechanisms is that the apparatus required to lock the switch in the closed or open position must be attached to each switch in a stationary manner. The parts that are required in order to make the switch lock in the closed or open position are not readily transportable from switch to switch. Thus the employment of these mechanisms is expensive where a large number of switches are involved, since a separate lock is needed for each switch, and the cost increases as the size of the switches increase. Such mechanisms would also be difficult, or in some cases impossible, to retrofit to existing switches.
One particular class of switches where safety technology is not well developed is the high-voltage and extra high-voltage air break switches that are typically employed by electric utility companies at power substations. These types of switches open and close through the rotation of an operating pipe. The pipe is often rotated by means of a gear driven motor drive, and the motor is activated by electronic controls. Since the switches are connected to a motor, they cannot be opened or closed without activation of a control signal (either through a nearby panel or remotely). The switches may be inadvertently opened or closed, however, when they are disconnected or de-coupled from their motor drive assemblies for purposes of maintenance. In addition, there are several types of manual switches of this type, including swing-handle switches (which are operated manually by a lever) and gear-operated switches (which are opened and closed using a hand crank mechanism). All of these types of switches are generally located outdoors, and the inventors of the present invention have found that in some cases a gust of wind is sufficient to inadvertently close an air break switch once it is disconnected or de-coupled from its opening/closing drive assembly. Since these switches are used to relay large electrical currents at very high voltages, the inadvertent closing of such a switch when equipment or personnel are not prepared may, for example, cause serious bodily injury or damage to expensive distribution and transmission equipment. Because these systems are part of an automated electrical transmission and distribution grid, an inadvertent switch closing could also cause a cascade of automatic equipment shutdowns, such that a whole power grid or generating plant is affected. The problem is particularly acute with regard to switches at substations associated with nuclear power plants, since the restart of a nuclear power plant following a safety-related emergency shutdown is a time-consuming and expensive process. Such an occurrence may even impact the availability of power across the grid, resulting in blackouts of service.
The art does contain some devices intended to provide safety lock-out for high-voltage lines and devices. U.S. Pat. No. 5,823,321 to Leclerc teaches a remote-controlled locking device to aid persons performing maintenance on high-voltage transmission or distribution lines. The device incorporates a T-shaped piece that fits to the breaker blade, with a key mechanism that operates the latch on the device. Again, a significant disadvantage of this mechanism is that the lock apparatus must be constructed as an integral part of each switch, and in a typical transmission and distribution grid comprising many thousands of high-voltages switches, the cost of retrofitting the entire system to use such devices would make this solution unfeasible.
The art also contains a number of other devices intended for use in connection with the manipulation of high-voltage switches that are not of the air-break variety discussed herein. U.S. Pat. Nos. 6,541,717 and 5,451,730, to Roberts and Phillips, Sr., respectively, teach switch locking mechanisms for hookstick-controlled switches. U.S. Pat. No. 1,339,506 to Getts teaches a locking switch for another type of high-voltage switch. None of these devices are useable with respect to the air break switches commonly used today in power substations.
What is desired is a simple, inexpensive, reliable device to lock (or block open) high-voltage air break switches when the drive assembly used to open and close the switch, whether manual or motor-driven, is disconnected or de-coupled for maintenance. In addition, it would be desirable that such a device be capable of employment with a wide variety of air break switch designs, and be capable of being retrofitted to such air break switches that are currently used in electricity transmission and distribution substations. The device should be portable so that there is no need to install a lock on every switch where locking is desired. Further, it would be desirable to have such a device that can be readily installed and removed by maintenance personnel in a short amount of time, without specialized equipment or tools and without specialized additional training. These desires are achieved, and the limitations of the related art devices are overcome, in the present invention as described below.